The present invention relates to a process for producing a electrically conductive composite polymer article having an excellent electric conductivity and transparency. Process of the present invention is useful for production of Schottky-barrier diodes, and patterned electrodes.
Heretofore, there have been known typical electrically conductive polymers such as polyacetylene, polyparaphenylene, polyphenylene sulfide, polypyrrole and polythiophene. These polymers are utilized as p-type or n-type conductors by selecting dopants, and also as metallic conductors.
Examples of the use of the conductive polymers are, for instance, electrodes, cells, batteries, semiconductor elements, solar cells, shielding materials for electromagnetic waves, antistatic agents, and the like. In case of using the polymers for those uses, however, there is a defect that the polymers are difficult to process because they are insoluble and non-melting, and also there is a practical obstruction because the synthesized films form in polymers are opaque.
Polypyrroles are particularly attractive conductive polymers since they have a high conductivity and a stability in air. As is described in Gardini. Adv. Heterocycl. Chem., 15, 67 (1973), however, a polypyrrole so-called "pyrrole black" prepared by oxidizing pyrrole with, for instance, hydroperoxide in an acid solution is a powder material. Further in order to enhance its conductivity it is necessary to dope it with an electron acceptor such as a halogen atom or an electron donor such as an alkali after the preparation. In addition a molded article obtained by compression molding of the powder is brittle and opaque.
There has been also known an electrochemical polymerization by employing platinum or gold as an anode, as described in A. F. Diaz and K. K. Kanazawa, J.C.C.S. Chem. Comm. 1979, 635. According to this method, however, since an insoluble and non-melting polypyrrole is deposited on the anode surface, it is impossible to produce an article having a desired shape from the obtained polymer film because it is insoluble and non-melting. Thus, the polymer film peeled off the anode is usually used as it is.
As mentioned above, according to the prior methods the product has a poor utility because a desired shape cannot be obtained, and also the highly conductive product is black and opaque, and has a transmittance of not more than 1%. Accordingly even if coating with a transparent resin for preventing light scattering due to irregularity of the surface of the film, the light transmittance cannot be improved.
There have been known several processes for preparing Schottky-barrier diodes by employing electrically conductive polymer articles. For instance, Schottky-barrier diodes using polyacetylene as a conductive polymer material are disclosed in, for example, Japanese Unexamined Patent Publication (Tokkyo Kokai) Nos. 146284/1980, 129370/1981, 147486/1981 and 147687/1981, and the diodes using polypyrrole are described in, for example, Japanese Unexamined Patent Publication (Tokkyo Kokai) No. 63759/1984.
Polyacetylene, however, has defects that it is very unstable to oxygen or moisture and that it is degraded with the lapse of time. Accordingly Schottky-barrier devices of polyacetylene must be used in an oxygen and moisture free system. Also Shottky-barrier devices of polypyrroles have defects that processability of the devices is bad and that electric conductors having a large area cannot be obtained because only the electrochemical polymerization is known as a preparation method of the polypyrrole.
Heretofore, patterned electrodes have been prepared by applying photoresists such as photosensitive resins to insulating substrates coated with conductive materials such as copper, gold, indium oxide and tin oxide, irradiating ultraviolet rays to the photoresists through a photomask having a desired pattern to cure the photoresists, removing the non-cured portion of the photoresists, and then forming electric circuits by chemical etching. The process steps, however, are very complicated.
As mentioned hereinabove, pyrrole or an N-substituted pyrrole which is a heterocyclic compound can provide a highly electrically conductive polymer. However, since polymerization can be conducted only by the electrochemical polymerization, it is impossible to form a patterned circuit of the polypyrrole or poly-N-substituted-pyrrole on an insulating substrate.
An object of the invention is to provide an improved process for producing an electrically conductive composite polymer article having an excellent electric conductivity.
Another object of the invention is to provide a process for producing a Schottky-barrier diode having an excellent property and a desired area by employing the process of the production of the electrically conductive composite polymer article.
The other object of the invention is to provide a simple process for producing a patterned electrode by employing the process of the production of the electrically conductive composite polymer article.